Despite the aggressive scaling of silicon-based IC's over the past few decades, transistor characteristics have yet to improve so that ‘THz’-range (˜300 GHz-to-3 THz) circuits can be effectively designed using conventional techniques. The few attempts at signal generation at these frequencies in CMOS have produced only very small power levels (e.g., tens of nano-watts). Until recently, the terahertz frequency range (0.3-3 THz) has been mostly addressed by high mobility custom III-V processes, bulky and expensive nonlinear optics, or cryogenically cooled quantum cascade lasers. There is a broad range of applications that could benefit from efficient power generation that would allow high power generation and efficient radiation in CMOS. A low cost room temperature alternative could enable a wide range of applications in security, defense, ultra-high speed wireless communication, sensors, and biomedical imaging not currently accessible due to cost and size limitations.
Two major challenges to a fully integrated ‘THz’ signal source with high enough power for practical applications in CMOS are, 1) effective signal generation above transistor cut-off frequencies, and 2) efficient electromagnetic radiation out of silicon. Traditional methods to generate high-frequency signals above the fmax of devices, such as varactors, nonlinear transmission lines or push-push oscillators, and radiating through conventional tuned antennas all suffer from a lack of power scalability due to parasitic scaling, modeling inaccuracies leading to poor efficiency, and low power. Also radiation through traditional antennas (e.g., an integrated dipole in silicon) leads to leaky substrate modes that are often remedied with off-chip structures such as dielectric lenses.
There is a need for an efficient, low-cost, optionally tunable, high-power, stable sub-THz/THz integrated source that can operate at room-temperature.